Hi N900 and Maemo users... I'm here to see if someone has got my same problem.

Steps:
Go to Settings/Profile
Set max volume for SMS tone and tap the tone to ear it.
Now save and send you an SMS and shutdown the screen to let the phone play the SMS tone.
Probably you will notice that the SMS tone volume is softer than you set it.

If you try these steps please make me know what's your response!
Thank you all!

EDIT:
bug here: https://bugs.maemo.org/show_bug.cgi?id=12528